1. Field of the Invention
The present invention relates mainly to a movable body display device that gives a graphic display of the position and speed of watercraft and other movable bodies.
2. Background Information
In the past, in the field of watercraft, AIS (universal shipborne automatic identification system) and TT (target tracking) are known methods for acquiring the position and speed of other vessels. With AIS, vessels wirelessly send position information, navigation information, and so forth to their surroundings, and receive information sent by other vessels, thereby acquiring the position, speed, and so forth of the other vessels. TT involves sensing the position, speed, and so forth of a target located near the host vessel based on the change in past radar images.
Japanese Patent Nos. 4,965,035 (Patent Literature 1) and 4,925,525 (Patent Literature 2) disclose a display device for displaying the position, speed, and so forth of other vessels by using AIS and TT (ARPA). As shown in FIGS. 7A and 7B, with this type of display device, vessels are displayed using an AIS symbol 93 or a TT symbol 94. The triangular or round figure of the AIS symbol 93 or TT symbol 94 represents the position of a vessel. The line segment of the AIS symbol 93 or TT symbol 94 is the speed vector, which indicates the speed of the vessel.